In the field of word processing, certain data stream conventions have been devised to facilitate various editing, display, printing, or communication functions performed by a word processing station. Among the many conventions adopted in the history are revisable data streams and printable data streams.
Revisable data streams are stored, for example on a magnetic diskette, in such a way that they may be randomly accessed by page name or number for ease in editing and for processing portions of the document. This random accessing requires certain types of information to be available for each document page including the location of the boundaries between the pages on the diskette and the format of the page (e.g., tabs, fonts, and indents). The locations of the boundaries between the pages are typically stored on the diskette in a dedicated area called the named record index while the format is stored at the top of each page.
Printable data streams were devised to allow less complex output functions, including printing and communication, without the burdensome function of editing. Printable data streams are stored on a diskette sequentially without the aforementioned two types of information. To find a given page within the printable data stream, the stream must be read sequentially from the start of the document keeping track of page boundaries and of the page format information as it changes.
Heretofore, if a user wished to browse a printable data stream, for example to check the integrity of a document received over communication lines, they were left with two choices. A user could convert the printable data stream into a revisable data stream and then browse using a random access method, or a user could sequentially browse the printable data stream. The former method requires a time consuming conversion and may require the storage of two data streams for a single document. The latter method requires a document to be scanned from the beginning each time a new document page is accessed.
The time delays and inefficient storage allocation associated with document conversion and with sequential scanning become significant when the document is long, such as a report or legal brief. It is therefore desirable to expedite the access of specific pages of a sequentially stored document without substantially increasing storage requirements.